Class BasicComboBoxUI

Direct Known Subclasses:
MetalComboBoxUI, SynthComboBoxUI 
public class BasicComboBoxUI
extends ComboBoxUI

Basic UI implementation for JComboBox.

The combo box is a compound component which means that it is an aggregate of many simpler components. This class creates and manages the listeners on the combo box and the combo box model. These listeners update the user interface in response to changes in the properties and state of the combo box.

All event handling is handled by listener classes created with the createxxxListener() methods and internal classes. You can change the behavior of this class by overriding the createxxxListener() methods and supplying your own event listeners or subclassing from the ones supplied in this class.

For adding specific actions, overide installKeyboardActions to add actions in response to KeyStroke bindings. See the article How to Use Key Bindings

Nested Classes

Modifier and Type Class Description
class  BasicComboBoxUI.ComboBoxLayoutManager

This layout manager handles the 'standard' layout of combo boxes.
class  BasicComboBoxUI.FocusHandler

This listener hides the popup when the focus is lost.
class  BasicComboBoxUI.ItemHandler

This listener watches for changes to the selection in the combo box.
class  BasicComboBoxUI.KeyHandler

This listener checks to see if the key event isn't a navigation key.
class  BasicComboBoxUI.ListDataHandler

This listener watches for changes in the ComboBoxModel.
class  BasicComboBoxUI.PropertyChangeHandler

This listener watches for bound properties that have changed in the combo box.

Fields

Modifier and Type Field Description
protected JButton arrowButton

The arrow button that invokes the popup.
protected Dimension cachedMinimumSize

The cached minimum preferred size.
protected JComboBox<Object> comboBox

The instance of JComboBox.
protected CellRendererPane currentValuePane

Used to render the currently selected item in the combo box.
protected Component editor

The Component that the @{code ComboBoxEditor} uses for editing.
protected FocusListener focusListener

This protected field is implementation specific.
protected boolean hasFocus

This protected field is implementation specific.
protected boolean isMinimumSizeDirty

The flag for recalculating the minimum preferred size.
protected ItemListener itemListener

This protected field is implementation specific.
protected KeyListener keyListener

This protected field is implementation specific.
protected JList<Object> listBox

This list is for drawing the current item in the combo box.
protected ListDataListener listDataListener

This protected field is implementation specific.
protected Insets padding

If specified, these insets act as padding around the cell renderer when laying out and painting the "selected" item in the combo box.
protected ComboPopup popup

The implementation of ComboPopup that is used to show the popup.
protected KeyListener popupKeyListener

The KeyListener listens to events.
protected MouseListener popupMouseListener

The MouseListener listens to events.
protected MouseMotionListener popupMouseMotionListener

The MouseMotionListener listens to events.
protected PropertyChangeListener propertyChangeListener

This protected field is implementation specific.
protected boolean squareButton

Indicates whether or not the combo box button should be square.

Constructors

Constructor Description
BasicComboBoxUI()

Methods

Modifier and Type Method Description
void addEditor()

This public method is implementation specific and should be private.
void configureArrowButton()

This public method is implementation specific and should be private.
protected void configureEditor()

This protected method is implementation specific and should be private.
protected JButton createArrowButton()

Creates a button which will be used as the control to show or hide the popup portion of the combo box.
protected ComboBoxEditor createEditor()

Creates the default editor that will be used in editable combo boxes.
protected FocusListener createFocusListener()

Creates a FocusListener which will be added to the combo box.
protected ItemListener createItemListener()

Creates an ItemListener which will be added to the combo box.
protected KeyListener createKeyListener()

Creates a KeyListener which will be added to the combo box.
protected LayoutManager createLayoutManager()

Creates a layout manager for managing the components which make up the combo box.
protected ListDataListener createListDataListener()

Creates a list data listener which will be added to the ComboBoxModel.
protected ComboPopup createPopup()

Creates the popup portion of the combo box.
protected PropertyChangeListener createPropertyChangeListener()

Creates a PropertyChangeListener which will be added to the combo box.
protected ListCellRenderer<Object> createRenderer()

Creates the default renderer that will be used in a non-editiable combo box.
static ComponentUI createUI​(JComponent c)

Constructs a new instance of BasicComboBoxUI.
int getBaseline​(JComponent c, int width, int height)

Returns the baseline.
Component.BaselineResizeBehavior getBaselineResizeBehavior​(JComponent c)

Returns an enum indicating how the baseline of the component changes as the size changes.
protected Dimension getDefaultSize()

Return the default size of an empty display area of the combo box using the current renderer and font.
protected Dimension getDisplaySize()

Returns the calculated size of the display area.
protected Insets getInsets()

Gets the insets from the JComboBox.
Dimension getMinimumSize​(JComponent c)

The minimum size is the size of the display area plus insets plus the button.
protected Dimension getSizeForComponent​(Component comp)

Returns the size a component would have if used as a cell renderer.
protected void installComponents()

Creates and initializes the components which make up the aggregate combo box.
protected void installDefaults()

Installs the default colors, default font, default renderer, and default editor into the JComboBox.
protected void installKeyboardActions()

Adds keyboard actions to the JComboBox.
protected void installListeners()

Creates and installs listeners for the combo box and its model.
boolean isFocusTraversable​(JComboBox<?> c)

Determines if the JComboBox is focus traversable.
protected boolean isNavigationKey​(int keyCode)

Returns whether or not the supplied keyCode maps to a key that is used for navigation.
boolean isPopupVisible​(JComboBox<?> c)

Tells if the popup is visible or not.
void paintCurrentValue​(Graphics g, Rectangle bounds, boolean hasFocus)

Paints the currently selected item.
void paintCurrentValueBackground​(Graphics g, Rectangle bounds, boolean hasFocus)

Paints the background of the currently selected item.
protected Rectangle rectangleForCurrentValue()

Returns the area that is reserved for drawing the currently selected item.
void removeEditor()

This public method is implementation specific and should be private.
protected void selectNextPossibleValue()

Selects the next item in the list.
protected void selectPreviousPossibleValue()

Selects the previous item in the list.
void setPopupVisible​(JComboBox<?> c, boolean v)

Hides the popup.
protected void toggleOpenClose()

Hides the popup if it is showing and shows the popup if it is hidden.
void unconfigureArrowButton()

This public method is implementation specific and should be private.
protected void unconfigureEditor()

This protected method is implementation specific and should be private.
protected void uninstallComponents()

The aggregate components which comprise the combo box are unregistered and uninitialized.
protected void uninstallDefaults()

Uninstalls the default colors, default font, default renderer, and default editor from the combo box.
protected void uninstallKeyboardActions()

Removes the focus InputMap and ActionMap.
protected void uninstallListeners()

Removes the installed listeners from the combo box and its model.

Methods declared in class javax.swing.plaf.ComponentUI

contains, getAccessibleChild, getAccessibleChildrenCount, getMaximumSize, getPreferredSize, installUI, paint, uninstallUI, update

Methods declared in class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Fields

comboBox

protected JComboBox<Object> comboBox

The instance of JComboBox.

hasFocus

protected boolean hasFocus

This protected field is implementation specific. Do not access directly or override.

listBox

protected JList<Object> listBox

This list is for drawing the current item in the combo box.

currentValuePane

protected CellRendererPane currentValuePane

Used to render the currently selected item in the combo box. It doesn't have anything to do with the popup's rendering.

protected ComboPopup popup

The implementation of ComboPopup that is used to show the popup.

editor

protected Component editor

The Component that the @{code ComboBoxEditor} uses for editing.

arrowButton

protected JButton arrowButton

The arrow button that invokes the popup.

keyListener

protected KeyListener keyListener

This protected field is implementation specific. Do not access directly or override. Override the listener construction method instead.

See Also:
createKeyListener()

focusListener

protected FocusListener focusListener

This protected field is implementation specific. Do not access directly or override. Override the listener construction method instead.

See Also:
createFocusListener()

propertyChangeListener

protected PropertyChangeListener propertyChangeListener

This protected field is implementation specific. Do not access directly or override. Override the listener construction method instead.

See Also:
createPropertyChangeListener()

itemListener

protected ItemListener itemListener

This protected field is implementation specific. Do not access directly or override. Override the listener construction method instead.

See Also:
createItemListener()

popupMouseListener

protected MouseListener popupMouseListener

The MouseListener listens to events.

popupMouseMotionListener

protected MouseMotionListener popupMouseMotionListener

The MouseMotionListener listens to events.

popupKeyListener

protected KeyListener popupKeyListener

The KeyListener listens to events.

listDataListener

protected ListDataListener listDataListener

This protected field is implementation specific. Do not access directly or override. Override the listener construction method instead.

See Also:
createListDataListener()

isMinimumSizeDirty

protected boolean isMinimumSizeDirty

The flag for recalculating the minimum preferred size.

cachedMinimumSize

protected Dimension cachedMinimumSize

The cached minimum preferred size.

squareButton

protected boolean squareButton

Indicates whether or not the combo box button should be square. If square, then the width and height are equal, and are both set to the height of the combo minus appropriate insets.

Since:
1.7

padding

protected Insets padding

If specified, these insets act as padding around the cell renderer when laying out and painting the "selected" item in the combo box. These insets add to those specified by the cell renderer.

Since:
1.7

Constructors

BasicComboBoxUI

public BasicComboBoxUI()

Methods

createUI

public static ComponentUI createUI(JComponent c)

Constructs a new instance of BasicComboBoxUI.

Parameters:
c - a component
Returns:
a new instance of BasicComboBoxUI

installDefaults

protected void installDefaults()

Installs the default colors, default font, default renderer, and default editor into the JComboBox.

installListeners

protected void installListeners()

Creates and installs listeners for the combo box and its model. This method is called when the UI is installed.

uninstallDefaults

protected void uninstallDefaults()

Uninstalls the default colors, default font, default renderer, and default editor from the combo box.

uninstallListeners

protected void uninstallListeners()

Removes the installed listeners from the combo box and its model. The number and types of listeners removed and in this method should be the same that was added in installListeners

createPopup

protected ComboPopup createPopup()

Creates the popup portion of the combo box.

Returns:
an instance of ComboPopup
See Also:
ComboPopup

createKeyListener

protected KeyListener createKeyListener()

Creates a KeyListener which will be added to the combo box. If this method returns null then it will not be added to the combo box.

Returns:
an instance KeyListener or null

createFocusListener

protected FocusListener createFocusListener()

Creates a FocusListener which will be added to the combo box. If this method returns null then it will not be added to the combo box.

Returns:
an instance of a FocusListener or null

createListDataListener

protected ListDataListener createListDataListener()

Creates a list data listener which will be added to the ComboBoxModel. If this method returns null then it will not be added to the combo box model.

Returns:
an instance of a ListDataListener or null

createItemListener

protected ItemListener createItemListener()

Creates an ItemListener which will be added to the combo box. If this method returns null then it will not be added to the combo box.

Subclasses may override this method to return instances of their own ItemEvent handlers.

Returns:
an instance of an ItemListener or null

createPropertyChangeListener

protected PropertyChangeListener createPropertyChangeListener()

Creates a PropertyChangeListener which will be added to the combo box. If this method returns null then it will not be added to the combo box.

Returns:
an instance of a PropertyChangeListener or null

createLayoutManager

protected LayoutManager createLayoutManager()

Creates a layout manager for managing the components which make up the combo box.

Returns:
an instance of a layout manager

createRenderer

protected ListCellRenderer<Object> createRenderer()

Creates the default renderer that will be used in a non-editiable combo box. A default renderer will used only if a renderer has not been explicitly set with setRenderer.

Returns:
a ListCellRender used for the combo box
See Also:
JComboBox.setRenderer(javax.swing.ListCellRenderer<? super E>)

createEditor

protected ComboBoxEditor createEditor()

Creates the default editor that will be used in editable combo boxes. A default editor will be used only if an editor has not been explicitly set with setEditor.

Returns:
a ComboBoxEditor used for the combo box
See Also:
JComboBox.setEditor(javax.swing.ComboBoxEditor)

installComponents

protected void installComponents()

Creates and initializes the components which make up the aggregate combo box. This method is called as part of the UI installation process.

uninstallComponents

protected void uninstallComponents()

The aggregate components which comprise the combo box are unregistered and uninitialized. This method is called as part of the UI uninstallation process.

addEditor

public void addEditor()

This public method is implementation specific and should be private. do not call or override. To implement a specific editor create a custom ComboBoxEditor

See Also:
createEditor(), JComboBox.setEditor(javax.swing.ComboBoxEditor), ComboBoxEditor

removeEditor

public void removeEditor()

This public method is implementation specific and should be private. do not call or override.

See Also:
addEditor()

configureEditor

protected void configureEditor()

This protected method is implementation specific and should be private. do not call or override.

See Also:
addEditor()

unconfigureEditor

protected void unconfigureEditor()

This protected method is implementation specific and should be private. Do not call or override.

See Also:
addEditor()

configureArrowButton

public void configureArrowButton()

This public method is implementation specific and should be private. Do not call or override.

See Also:
createArrowButton()

unconfigureArrowButton

public void unconfigureArrowButton()

This public method is implementation specific and should be private. Do not call or override.

See Also:
createArrowButton()

createArrowButton

protected JButton createArrowButton()

Creates a button which will be used as the control to show or hide the popup portion of the combo box.

Returns:
a button which represents the popup control

isPopupVisible

public boolean isPopupVisible(JComboBox<?> c)

Tells if the popup is visible or not.

Specified by:
isPopupVisible in class ComboBoxUI
Parameters:
c - a JComboBox
Returns:
true if popup of the JComboBox is visible

setPopupVisible

public void setPopupVisible(JComboBox<?> c,
                            boolean v)

Hides the popup.

Specified by:
setPopupVisible in class ComboBoxUI
Parameters:
c - a JComboBox
v - a boolean determining the visibilty of the popup

isFocusTraversable

public boolean isFocusTraversable(JComboBox<?> c)

Determines if the JComboBox is focus traversable. If the JComboBox is editable this returns false, otherwise it returns true.

Specified by:
isFocusTraversable in class ComboBoxUI
Parameters:
c - a JComboBox
Returns:
true if the given JComboBox is traversable

getMinimumSize

public Dimension getMinimumSize(JComponent c)

The minimum size is the size of the display area plus insets plus the button.

Overrides:
getMinimumSize in class ComponentUI
Parameters:
c - the component whose minimum size is being queried; this argument is often ignored, but might be used if the UI object is stateless and shared by multiple components
Returns:
a Dimension object or null
See Also:
JComponent.getMinimumSize(), LayoutManager.minimumLayoutSize(java.awt.Container), ComponentUI.getPreferredSize(javax.swing.JComponent)

getBaseline

public int getBaseline(JComponent c,
                       int width,
                       int height)

Returns the baseline.

Overrides:
getBaseline in class ComponentUI
Parameters:
c - JComponent baseline is being requested for
width - the width to get the baseline for
height - the height to get the baseline for
Returns:
baseline or a value < 0 indicating there is no reasonable baseline
Throws:
NullPointerException - if c is null
IllegalArgumentException - if width or height is < 0
Since:
1.6
See Also:
JComponent.getBaseline(int, int)

getBaselineResizeBehavior

public Component.BaselineResizeBehavior getBaselineResizeBehavior(JComponent c)

Returns an enum indicating how the baseline of the component changes as the size changes.

Overrides:
getBaselineResizeBehavior in class ComponentUI
Parameters:
c - JComponent to return baseline resize behavior for
Returns:
an enum indicating how the baseline changes as the component size changes
Throws:
NullPointerException - if c is null
Since:
1.6
See Also:
JComponent.getBaseline(int, int)

isNavigationKey

protected boolean isNavigationKey(int keyCode)

Returns whether or not the supplied keyCode maps to a key that is used for navigation. This is used for optimizing key input by only passing non- navigation keys to the type-ahead mechanism. Subclasses should override this if they change the navigation keys.

Parameters:
keyCode - a key code
Returns:
true if the supplied keyCode maps to a navigation key

selectNextPossibleValue

protected void selectNextPossibleValue()

Selects the next item in the list. It won't change the selection if the currently selected item is already the last item.

selectPreviousPossibleValue

protected void selectPreviousPossibleValue()

Selects the previous item in the list. It won't change the selection if the currently selected item is already the first item.

toggleOpenClose

protected void toggleOpenClose()

Hides the popup if it is showing and shows the popup if it is hidden.

rectangleForCurrentValue

protected Rectangle rectangleForCurrentValue()

Returns the area that is reserved for drawing the currently selected item.

Returns:
the area that is reserved for drawing the currently selected item

getInsets

protected Insets getInsets()

Gets the insets from the JComboBox.

Returns:
the insets

paintCurrentValue

public void paintCurrentValue(Graphics g,
                              Rectangle bounds,
                              boolean hasFocus)

Paints the currently selected item.

Parameters:
g - an instance of Graphics
bounds - a bounding rectangle to render to
hasFocus - is focused

paintCurrentValueBackground

public void paintCurrentValueBackground(Graphics g,
                                        Rectangle bounds,
                                        boolean hasFocus)

Paints the background of the currently selected item.

Parameters:
g - an instance of Graphics
bounds - a bounding rectangle to render to
hasFocus - is focused

getDefaultSize

protected Dimension getDefaultSize()

Return the default size of an empty display area of the combo box using the current renderer and font.

Returns:
the size of an empty display area
See Also:
getDisplaySize()

getDisplaySize

protected Dimension getDisplaySize()

Returns the calculated size of the display area. The display area is the portion of the combo box in which the selected item is displayed. This method will use the prototype display value if it has been set.

For combo boxes with a non trivial number of items, it is recommended to use a prototype display value to significantly speed up the display size calculation.

Returns:
the size of the display area calculated from the combo box items
See Also:
JComboBox.setPrototypeDisplayValue(E)

getSizeForComponent

protected Dimension getSizeForComponent(Component comp)

Returns the size a component would have if used as a cell renderer.

Parameters:
comp - a Component to check
Returns:
size of the component
Since:
1.7

installKeyboardActions

protected void installKeyboardActions()

Adds keyboard actions to the JComboBox. Actions on enter and esc are already supplied. Add more actions as you need them.

uninstallKeyboardActions

protected void uninstallKeyboardActions()

Removes the focus InputMap and ActionMap.

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https://docs.oracle.com/en/java/javase/11/docs/api/java.desktop/javax/swing/plaf/basic/BasicComboBoxUI.html